Electro-thermal mechanical testing (ETMT) with direct current and Joule heating was used to study the dissolution and formation of \(\gamma '\) precipitates in miniaturised samples of the single crystal nickel-base superalloys, CMSX4 and CMSX10N. Alloys were subjected to heating and cooling cycles with resistivity simultaneously measured to infer \(\gamma \leftrightarrow \gamma '\) phase transformations. Temperature-resolved resistivity measurements exhibit notable variations between samples; however, when normalized, the resistivity changes become systematic, with trends suitable to infer phase transformation behaviour. Specifically, dissolution and precipitation behaviour of the \(\gamma '\) phase with respect to heating or cooling rates can be determined. The ETMT measured \(\gamma '\) solvus is lower compared with the calorimetric/thermodynamic value and approaches the latter, when the resistivity values exceed a threshold value, which is temperature dependent. The differences in the resistivity curves cannot be explained by the range in \(\gamma '\) size distribution within the specimens; rather, the difference becomes prominent above a threshold current density, which occurs above a given temperature. Like in the case of dissolution, the nucleation and precipitation of \(\gamma '\) is dependent on the normalized resistivity, but independent of stress, if cooling occurs under restraints in case of the latter. A greater \(\gamma '\) solvus corresponds to an increased nucleation temperature, implying a varying undercooling for nucleation when calculated with respect to the thermodynamic solvus. When stress develops during cooling, it increases rapidly above a critical \(\gamma '\) mole-fraction when precipitation hardening becomes prominent. Given these features are endemic to ETMT, some guidelines are offered for use of ETMT tests in specific applications.
